1. Field of the Invention
The present invention generally relates to a method for fabricating devices on semiconductor substrates. More specifically, the invention relates to a method for fabricating a magneto-resistive random access memory (MRAM) device.
2. Description of the Related Art
Microelectronic devices are generally fabricated on a semiconductor substrate as integrated circuits wherein various conductive layers are interconnected to one another to facilitate propagation of electronic signals within the device. An example of such a device is a storage element in memories such as magneto-resistive random access memories (MRAM) that facilitate storage of digital information.
A memory cell in a MRAM device is a multi-layered structure comprising two sets of magnetic layers separated by a non-magnetic dielectric material. These layers are deposited as overlying blanket films, and then patterned to form the MRAM device. More specifically, the MRAM device comprises a top electrode layer (e.g., tantalum (Ta), tantalum nitride (TaN), and the like), a free magnetic layer (e.g., NiFe, CoFe, and the like), a tunnel layer (e.g., Al2O3, and the like), a multi-layer magnetic stack comprising layers of cobalt-iron alloy (CoFe), ruthenium (Ru), platinum-manganese alloy (PtMn), and the like, a bottom electrode (e.g., Ta, TaN, and the like), and a barrier layer (e.g., SiO2, and the like).
Fabrication of a MRAM device comprises plasma etch processes in which one or more layers of a MRAM film stack are removed, either partially or in total. The MRAM film stack comprises materials that are sensitive to corrosion and may be easily eroded, oxidized, or damaged during device fabrication, as well as develop difficult to remove metal-containing residues. Such residues generally build up along the sides of the MRAM film stack and may form a veil-like pattern. The conductive residues or eroded layers may cause electrical short-circuits within the MRAM film stack.
The magnetic materials of the multi-layer magnetic stack are generally etched using predominantly physical plasma processes, such as ion milling, sputtering, and the like. Such etch processes have low etch rates for magnetic materials (e.g., CoFe, Ru, PtMn, and the like) and typically produce metal-containing residues. Removal of such residues are time-consuming routines that decrease productivity and increase the cost of fabricating the MRAM devices.
Therefore, there is a need in the art for an improved method of etching magnetic materials for fabrication of a magneto-resistive random access memory (MRAM) device.